Error Handling #8
https://doc.rust-lang.org/book/error-handling.html
Reading from stdinの手前まででビルド通った。
extern crate getopts; extern crate rustc_serialize; extern crate csv; use getopts::Options; use std::env; use std::fs::File; use std::path::Path; use std::error::Error; // This struct represents the data in each row of the CSV file. // Type based decoding absolves us of a lot of the nitty gritty error // handling, like parsing strings as integers or floats. #[derive(Debug, RustcDecodable)] struct Row { country: String, city: String, accent_city: String, region: String, // Not every row has data for the population, latitude or longitude! // So we express them as `Option` types, which admits the possibility of // absence. The CSV parser will fill in the correct value for us. population: Option<u64>, latitude: Option<f64>, longitude: Option<f64>, } struct PopulationCount { city: String, country: String, // This is no longer an `Option` because values of this type are only // constructed if they have a population count. count: u64, } fn print_usage(program: &str, opts: Options) { println!("{}", opts.usage(&format!("Usage: {} [options] <data-path> <city>", program))); } fn search<P: AsRef<Path>> (file_path: P, city: &str) -> Result<Vec<PopulationCount>, Box<Error>> { let mut found = vec![]; let file = try!(File::open(file_path)); let mut rdr = csv::Reader::from_reader(file); for row in rdr.decode::<Row>() { let row = try!(row); match row.population { None => { } // Skip it. Some(count) => if row.city == city { found.push(PopulationCount { city: row.city, country: row.country, count: count, }); }, } } if found.is_empty() { Err(From::from("No matching cities with a population were found.")) } else { Ok(found) } } fn main() { let args: Vec<String> = env::args().collect(); let program = &args[0]; let mut opts = Options::new(); opts.optflag("h", "help", "Show this usage message."); let matches = match opts.parse(&args[1..]) { Ok(m) => { m } Err(e) => { panic!(e.to_string()) } }; if matches.opt_present("h") { print_usage(&program, opts); return; } let data_path = &matches.free[0]; let city: &str = &matches.free[1]; match search(data_path, city) { Ok(pops) => { for pop in pops { println!("{}, {}: {:?}", pop.city, pop.country, pop.count); } } Err(err) => println!("{}", err) } }